The present invention generally relates to hearing devices worn by a person to improve the person's ability to hear sounds. Reference will sometimes be made herein to “hearing aids;” however, such references are not intended to limit the invention to use by persons having hearing loss. The invention could as well be used by persons without hearing impairments.
The invention more particularly relates to hearing devices wherein at least a portion of the device occludes the ear canal and creates undesirable insertion effects. The invention has particular applicability to open ear hearing devices, but could also be used in conjunction with closed ear devices.
Inserting all or a portion of a hearing aid into the ear distorts both the magnitude and phase of the sound arriving at the ear drum. Ideally, the hearing device will compensate for these effects so that the arriving sound remains undistorted after passing through the hearing device and ear canal. Many hearing aid devices compensate for the magnitude effects, but fail to adequately address phase distortion. The result is that users often complain that the sound is not natural and lacks directional cues important to the listening experience. Such complaints are particularly prevalent among musicians and professionals in the music industry, whose ears are trained to distinguish subtle differences but who require hearing aids to compensate for a partial loss of hearing.
One proposed solution of compensating for the insertion effect of hearing aids is described in U.S. Pat. No. 5,325,436 to Sigfrid Soli, et al. The Soli patent discloses a method of determining a digital filter that compensates for the insertion effects of an in-ear hearing aid. In Soli the magnitude and phase response in the ear is measured both without the hearing aid and with the hearing aid in place. The required equalization (EQ) is then calculated. In doing so, Soli makes assumptions regarding the phase component that in most cases are not valid. The method described by Soli is complicated, requires that the EQ be calculated, and due to the assumptions made about phase is likely to be ineffective. Soli pre-supposes an ear piece that fully occludes the ear canal so as to attenuate all outside sounds. Also, the correction described in Soli is intended only to preserve the interaural timing difference between the ears, not the absolute timing difference: because of this, Soli requires binaural fittings of the hearing aids.
The present invention provides a device and method for correcting the insertion effect of a hearing device in an ear, which requires no assumptions about the phase response, can be used with monaural fittings, and is suited for open ear inserts. The invention is particularly effective in correcting, at the ear drum, phase distortion and anomalies in sound caused by the presence of the hearing device in the ear canal. The device and method of the invention are capable of providing, to the ear drum, amplified sound that is perceived as natural and which retains directional cues for an improved listening experience; that is, the device is perceived to be acoustically transparent. Improvements to the listening experience will be realized by most users, but will be realized in particular by music industry professionals who wish to regain their capability to discern subtle musical differences.